1. Field of the Invention
The present invention relates to agricultural irrigation. More particularly, the present invention relates to a tubular flexible hose, or tape, which is used to distribute water substantially uniformly at discreet locations spaced along its length. Such "tape" hoses are creased longitudinally so that when they are not filled with water under pressure they collapse to a flat tape-like configuration. Such tapes are more easily rolled, transported, and stored than are hoses which remain always round in cross section. Consequently, the present invention relates to hose structure of the type generally recognized as "drip irrigation tape". Such drip irrigation tapes are widely used in row-crop farming so that irrigation water is distributed to the soil immediately adjacent to the growing plants, and the entire field need not be irrigated. The use of such irrigation tapes results in considerable reduction in water use, loss of fertilizer, and accumulation of mineral salts in arable agricultural soils.
2. Related Technology
A conventional hose for irrigation use is known in accord with U.S. Pat. No. 4,047,995, issued 13 Sep. 1977. This conventional irrigation hose is made from an elongate strip of thin plastic film which is either folded or wrapped sealingly on itself, or with a similar strip of plastic film, so that two layers of the plastic film are partially or fully overlapped and sealed together in facial contact. The strip or strips of plastic film form an elongate primary flow path along which a large-volume flow of irrigation water may pass. In order to provide plural small drip-like water flows outwardly of the hose, the plastic film is not sealed to itself, or to the other strip of plastic film, in selected areas spaced along the length of the hose. These areas define elongate tortuous patterns communicating from the primary flow path outwardly of the hose. Consequently, when the hose is supplied internally with pressurized water, the areas where the plastic film is not sealed together separate slightly to form secondary drip flow paths and to allow water to seep between the layers of plastic film to plural spaced-apart fine-dimension outlets on the hose at which a dripping water flow may take place. That is, the areas where the plastic film is not sealed either to itself or to the similar strip of plastic film defines plural fine-dimension tortuous, serpentine, or elongate and constricted secondary flow paths spaced along the length of the hose and each leading from the longitudinal primary water flow path outwardly to respective spaced-apart outlet ports along the length of the hose.
With an irrigation hose according to the '995 patent, the rate of dripping water flow from the outlets of the hose decreases along a length of the hose as the water pressure within the hose decreases. This decrease in water pressure level in inescapable because of friction resulting from the flow of the water, and the fact that water volume in the hose decreases as the water is metered out through the dripping outlets. The result is that irrigated plants near the water inlet end of the hose may receive an excess of water. Near the center of a run of this hose, the irrigated plants may receive the desired amount of water, and near the far end of the hose away from the water inlet, the irrigated plants will receive too little water.
Also, the size of the tortuous or serpentine passages through which dripping water flow must escape the hose are so small that they are easily clogged by debris and particulates in the hose. Moreover, the water used for irrigation purposes may not be (and generally will not be) potable water. Consequently, this water will frequently carry bacterial slime, algae, and particulates which can quickly plug the small metering passages of a hose like that taught by the '995 patent. Further, because these metering passages only really open when the hose is pressurized, and are otherwise closed, once they become clogged they will remain clogged. Relief of internal water pressure on this hose has the effect of allowing the drip passages to constrict and trap clogging contaminants in these passages. Further, the inlets to the tortuous metering drip passages of this hose are disposed at a crevice or bite between the overlapped sheets of plastic film. Consequently, the primary water flow is not particularly vigorous or turbulent as it passes these inlets. Again, the result is a hose with drip outlets which clog easily and which will not unclog. Finally, this hose provides outlet openings on the hose which allow reflux of environmental water and contamination into the metering passages. This reflux of water and contamination may clog the dripping outlets. Also, small plant roots may find their way into the outlets on the hose, and again may clog the dripping outlets.
Another conventional drip irrigation hose which attempts to solve the problem of inconsistent water outlet dripping flow rate along the length of a run of the hose is known in accord with U.S. Pat. No. 4,009,832, issued 1 Mar. 1977. The hose taught by the '832 patent the primary water flow path is made by an elongate strip or strips of plastic film which are partially or fully overlapped and sealed together to form a primary water flow path. An inner flap or inner wall portion of the hose cooperates with an outer wall portion of the hose to define a throttling gap. This structure results in a drip irrigation hose which is more nearly uniform in its rate of water delivery despite varying pressure over a length of the hose.
However, consideration of the structure for the drip irrigation hoses set forth in the '832 patent will reveal that this hose suffers from many of the deficiencies described above with respect to the hose of the '995 patent. For example, even though the '832 patent asserts that the hose is self cleaning with respect to being able to flush out contaminants (i.e., slime, algae, and particulates) because the flap portion of the inner wall will open up the metering or throttling gap when the hose is open for flushing, it is seen that the inlets from the primary flow path of this hose to the secondary flow path and drip outlets is still defined either at a crevice or bite along the length of the hose, or as simple holes perforating the inner wall perpendicularly to the axis of the primary flow path. Primary water flow at these inlets to the secondary flow paths will be rather sluggish and contaminants can easily enter these inlets. Further, flushing of the hose to remove contaminants clogging the secondary flow paths can have only a limited effect because the flap portion of the hose wall inherently must have an initial contacting relationship with the overlying wall portion even when the hose in not under pressure. Were the hose constructed otherwise, this flap portion would not form a pressure drop for the metered water flow and would not be urged into metering relationship with the outer wall of the hose. Consequently, this flap will not in fact move out of engagement with the overlying wall portion of the hose sufficiently to release clogging contaminants.
Yet another conventional drip irrigation hose is known in accord with U.S. Pat. No. 4,247,051, issued 27 Jan. 1981. The drip irrigation hose according to the '051 patent is formed similarly to the hoses discussed above, with modifications directed to reducing clogging of the drip outlets of the hose. More particularly, the size of the tortuous, serpentine, or elongate and restrictively small sized secondary flow passages extending between the primary water flow path of the hose and the drip outlets of the hose are increased so that it is not so easily clogged by contaminants. However, the flow rate of water through the secondary flow paths is controlled by the configuration of these pathways so that water drip flow rates are maintained. The hose is formed with elongate ribs spacing the overlapped walls of the secondary metering flow path away from one another. These ribs may be formed by adhesively securing a non-adhesive elongate spacer, such as a monofilament fishing line, between the overlapped walls of the hose.
An assertion for the hose provided by the '051 patent is that the inlet and outlet holes of the secondary metering passages may be of sufficient size as to not easily clog. Also, the water flow velocity in the secondary metering passages is asserted to be sufficiently high that self-cleaning of the inlet and outlet holes is provided. However, a close consideration of the structure presented by the '051 patent suggests that the objectives for this irrigation hose may not be realized in fact. Slotted intake opening to the secondary flow paths are provided in one embodiment of this patent, with no particular explanation of why these slotted openings would not themselves clog with contaminants. A flexible flap type of outlet valve is provided also by an embodiment of this invention, which valve is configured so that it presents a flow constriction and may not open wide in the event it becomes partially clogged, so that the clogging material would be ejected. The result is that the outlet valve could easily clog and the irrigation hose of the '051 patent includes features which defeat the purpose of providing an irrigation hose with reduced clogging.
Still another conventional irrigation hose is known in accord with U.S. Pat. No. 4,722,759, issued 2 Feb. 1988. This irrigation hose provides a longitudinal primary flow path communicating with a longitudinal secondary flow path via spaced apart inlets which are controlled by an inner flap portion of the overlapped walls of the hose to throttle water flow responsive to the local pressure level of the water. At spaced apart drip outlets of this hose, the overlapped walls of the hose have a respective break in a longitudinal heat-sealed seam between the overlapped walls. Consequently, the walls of the hose may separate slightly to allow water outflow at these outlets to the crops to be irrigated. Similarly to the irrigation hoses considered above, however, the hose of the '759 patent defines inlets to the secondary flow paths which are at a crevice or bite internally of the hose. Again, primary water flow at these inlets could not be vigorous under normal irrigation use conditions for the hose. Accordingly, frequent clogging of these inlets to the secondary flow paths could be expected with this hose.
Additional conventional drip irrigation hoses or tapes are known in accord with U.S. Pat. Nos. 4,548,360, issued 22 Oct. 1985; 5,118,042, issued 2 Jun. 1992; 5,192,027, issued 9 Mar. 1992; and 5,252,162, issued 12 Oct. 1993, all of which are assigned to the assignee of the present application.
In view of the interest in developing drip irrigation hoses which provide a more nearly constant irrigating water flow along a run of the hose despite the reduction in internal water flow pressure which occurs along a hose run, the California Agriculture Technology Institute has provided a formula by which the uniformity of water delivery may be measured. The Institute's publication No. 92100 sets out the formula Q=K(H).sup.x, where H is local primary water pressure (i.e., at the inlet end of a drip-flow path of the hose leading to a water outlet), Q is the rate of water flow from the drip-flow outlet of the hose, and K is a constant. If "x" falls in the range from 0.5 to 1.0, the hose is considered not to be pressure compensated. That is, the delivery rate of water from the drip-flow outlets of the hose is simply a function of the internal water pressure existing in the hose at particular locations along the length of a run. Such a hose has the classic problem of over watering plants near the inlet end of the hose and under watering plants at locations distant from this inlet end. If the value of "x" is less than 0.5, then the hose is considered to be pressure compensated, and the drip-flow irrigation rate is not simply a function of applied water pressure but is somewhat independent of the internal water pressure at particular locations along the length of a hose run. Such an irrigation hose provides a more uniform water delivery along the length of a long run of the hose. Ideally, if the value for "x" is zero the hose is fully pressure compensated, and the irrigating drip-flow rate would be constant irrespective of internal water pressure. Such an idealized irrigation hose does not exist.